Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

Carpal tunnel syndrome is a complex of symptoms as a result of compression of the median nerve in the carpal tunnel. As nerve entrapment induces impairment of somatic fibres followed by clinical symptoms and signs of the syndrome, one can assume that sympathetic fibres are involved too. Results of studies focused on this problem show presence of sympathetic symptoms in about half of patients, including Raynaud phenomenon, blanching of hands, painful swelling of fingers, dry or excessive sweating of palms. Activity of sympathetic system can be investigated by means of sympathetic skin response and vasomotor response. Eight papers presenting the results of sympathetic skin response from median nerve in carpal tunnel syndrome were analysed. Results of 4 studies showed decreased sympathetic activity, in 2 findings were equivocal and 2 studies failed to reveal any abnormalities. The following variables were considered in the interpretation of sympathetic skin response curve: amplitude, latency and area under the chart, each of them having limited diagnostic value due to inter-and intrasubject variation of these parameters. Vasomotor response was investigated in 2 studies by means of Doppler ultrasound flow examination in digital arteries. Results of both studies showed decreased vasomotor response in carpal tunnel syndrome. The review of current knowledge on sympathetic impairment in carpal tunnel syndrome fails to provide a definitive determination of its range and clinical consequences. It confirms, however, that routine examination of sympathetic disturbances is unnecessary due to their minor clinical significance.
What nerve is involved in carpal tunnel syndrome?